1 III STUDIES l\ IMMUNITY. 



It must be quite evident to the reader how olose an analogy there 

 is between the action of cholera serum and of this anticorpuseular 

 serum, the properties of which we have merely outlined. In the 

 preceding pages the description so much resembles the description 



of a specific cholera serum that it would hold for the latter if the 

 words "defibrinated Mood" were replaced by the words "culture 

 of vibrios" ami the expression "destruction of rabbit blood cells" 

 by the expression "granular transformation of the vibrio." The 

 analogy is still more striking when we consider that the alexin that 

 affects rabbit blood cells is probably identical with that which 

 causes a granular transformation of the vibrios. At least the 

 intense destructive power which is evident in both instances is 

 destroyed at 55 degrees. In both instances this destructive property 

 would seem to be widely distributed, not only in the serum but in 

 the peritoneal exudate, and it would seem to be absent from sub- 

 cutaneous edema fluid obtained by venous compression. If mix- 

 tures of defibrinated guinea-pig blood and rabbit serum are made 

 on the one hand and defibrinated blood and edema fluid from the 

 same rabbit on the other hand, it will be found that there is destruc- 

 tion of the guinea-pig corpuscles in the serum tube, but none in the 

 edema tube. As we already know edema fluid also fails to produce 

 a metamorphosis of vibrios treated with heated cholera serum. 



What conclusions may be drawn from these analogies? We 

 may conclude that the properties with which cholera serum is 

 endowed have not been manufactured by the animal body for the 

 simple purpose of combating an infection, if w r e may so express 

 it, but are due simply to the starting up of certain preexistent 

 functions that may be directed according to chance conditions either 

 against such harmful substances as vibrios or else against such 

 wholly innocuous elements as red blood cells. As we have already 

 shown, on injecting animals with harmless substances such as red 

 blood cells we obtain a serum which affects these cells just as a 

 cholera serum affects the cholera vibrio. In the case of the cholera 

 vibrio these properties do not arise spontaneously, expressly to 

 defend the animal against this organism, any more than does phago- 

 cytosis, the very keystone of immunity, owe its existence to a need 

 of combating bacterial infections. One of the most important 

 conclusions to be drawn from MetchnikofFs work is that immunity 



